In many technological fields, it is common practice to introduce holes into electrically conductive workpieces, e.g. metallic workpieces, where the diameter of the holes is a critical parameter. This is, in particular, true for gas turbine components such as, e.g., turbine vanes, turbine blades or components of thermal shieldings. In particular, in turbine blades or vanes as well as in shielding elements of a thermal shielding, such holes are often used for blowing cooling air out of the blade, vane or component, respectively. As the correct metering of air flowing through the holes is an important parameter for gas turbine operation, the diameter of the holes introduced into the blades, vanes or components needs to be precisely controlled. However, such a control requires the diameter of the hole to be precisely known.